NICKEL METAL HYDRIDE BATTERIES
Overview
Construction
As electronic products have come to feature more
sophisticated functions, more compact sizes and
lighter weights, the sources of power that operate
these products have been required to deliver in-
creasingly higher levels of energy. To meet this
requirement, nickel-metal hydride batteries have
been developed and manufactured with nickel hydro-
xide for the positive electrode and hydrogen-absorb-
ing alloys, capable of absorbing and releasing hydro-
gen at high-density levels, for the negative electrode.
Because Ni-MH batteries have about twice the
energy density of Ni-Cd batteries and a similar
operating voltage as that of Ni-Cd batteries, they are
expected to become a mainstay in the next genera-
tion of rechargeable batteries.
Nickel-metal hydride batteries consist of a positive
plate containing nickel hydroxide as its principal active
material, a negative plate mainly composed of hydro-
gen-absorbing alloys, a separator made of fine fibers,
an alkaline electrolyte, a metal case and a sealing
plate provided with a self-resealing safety vent. Their
basic structure is identical to that of Ni-Cd batteries.
With cylindrical nickel-metal hydride batteries, the
positive and negative plates are seperated by the
separator, wound into a coil, inserted into the case,
and sealed by the sealing plate through an electrically
insulated gasket.
With prismatic nickel-metal hydride batteries, the
positive and negative plates are sandwiched together
in layers with separators between them, inserted into
the case, and sealed by the sealing plate.
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NICKEL METAL HYDRIDE BATTERIES - CONTINUED
The hydrogen-absorbing alloy negative electrode
successfully reduces the gaseous oxygen given off
Features
•
Similarity with Ni-Cd batteries
These batteries have similar discharge characteris-
tics to those of Ni-Cd batteries.
from the positive electrode during overcharge by
sufficiently increasing the capacity of the negative
electrode which is the same method employed by Ni-
Cd batteries. By keeping the battery’s internal press-
ure constant in this manner, it is possible to seal the
battery.
•
Double the energy density of conventional
batteries
Nickel-metal hydride batteries have approximately
double the capacity compared with Panasonic’s
standard Ni-Cd batteries.
1.8
Charge
Size
Charge
: KR17/43
: 1CmA X 1.2h
H
O
OH
Ni
+
+
MHx
H
H
H
H
H
1.6
1.4
1.2
Discharge : 0.2CmA
Temperature: 20˚C
Discharge
O
OH
Ni
H
+
+
H
M
1.0
0.8
P-120AS
Ni-Cd
HHR160A
Ni-MH
HHR200A
Ni-MH
(Negative Electrode
Hydrogen-absorbing Alloy)
(Positive Electrode
Nickel Hydroxide)
0
200
400 600 800 1000 1200 1400 1600 1800 2000
Discharge Capacity (mAh)
•
Cycle life equivalent to 500 charge and
discharge cycles
Schematic Discharge of Ni-MH Battery
Like Ni-Cd batteries, nickel-metal hydride batteries
can be repeatedly charged and discharged for about
500 cycles. (example: IEC charge and discharge
conditions)
•
Rapid charge in approx. 1 hour
Nickel-metal hydride batteries can be rapidly
charged in about an hour using a specially designed
charger.
•
Excellent discharge characteristics
Since the internal resistance of nickel-metal hydride
batteries is low, continuous high-rate discharge up to
3CmA is possible, similar to Ni-Cd batteries.
2200
Size : HR17/43
Charge: 1CmA X 1.2h
Temp.: 20˚C
2000
HHR200A
Ni-MH
1800
1600
HHR160A
Ni-MH
1400
1200
P-120AS
Ni-Cd
1000
800
600
400
0
1
2
3
4
5
Discharge Current (A)
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NICKEL METAL HYDRIDE BATTERIES - CONTINUED
•
Charge temperature characteristics at various
charge rates
Five Main Characteristics
As with Ni-Cd batteries, nickel-metal hydride batteries
have five main characteristics: charge, discharge,
storage life, cycle life and safety.
110
1C
100
90
•
Charge characteristics
Like Ni-Cd batteries, the charge characteristics of nickel-
metal hydride batteries are affected by current, time and
temperature. The battery voltage rises when the charge
current is increased or when the temperature is low.
The charge efficiency differs depending on the current,
time, temperature and other factors.
Charge
0.33C
0.1C
80
0.1C x 12h
0.33C x 4h
1C x 1.2h
70
60
Discharge : 0.2C to 1.0V
Temperature: 20C
50
40
Model
: HHR160A
Nickel-metal hydride batteries should be charged at a
temperature ranging from 0°C to 40°C using a constant
current of 1C or less. The charge efficiency is
particularly good at a temperature of 10°C to 30°C.
Repeated charge at high or low temperatures causes
the battery performance to deteriorate. Furthermore,
repeated overcharge should be avoided since it will
downgrade the battery performance.
-10
0
10
20
30
40
50
60
70
Charge Temperature
•
Discharge characteristics
The discharge characteristics of nickel-metal hydride
batteries are affected by current, temperature, etc.,
and the discharge voltage characteristics are flat at
1.2V, which is almost the same as for Ni-Cd
batteries. The discharge voltage and discharge
efficiency decrease in proportion as the current rises
Refer to the section on recommended charge methods
for details on how to charge the batteries.
•
Charge characteristics
or the temperature drops.
As with Ni-Cd batteries,
charge and discharge of these batteries under
repeated
high
2.0
1.8
Charge
Temperature: 20C
Model : HHR160A
1C
: 120%
discharge cut-off voltage conditions (more than 1.1V
per cell) causes a drop in the discharge voltage
(which is sometimes accompanied by a
simultaneous drop in capacity). The discharge
characteristics can be restored by charge and
discharge to a discharge end voltage of down to 1.0V
per cell.
1.6
1.4
0.33C
0.1C
1.2
1.0
0.8
0.6
0
20
40
60
80
100 120
140
160
Charge Capacity (%) (Nominal Capacity Ratio)
•
Charge temperature characteristics at 1C charge
•
Discharge characteristics
2.0
Charge : 1CmA x 120%
Model : HHR160A
2.0
1.8
1.6
1.8
Charge
Temperature: 20C
Model : HHR160A
: 1CmA x 1.2h
0C
1.6
20C
40C
1.4
0.2C 1C 3C
1.4
1.2
1.2
1.0
0.8
1.0
0.8
0.6
0
20
40
60
80
100 120
140
160
Charge Capacity (%) (Nominal Capacity Ratio)
0.6
0
20
40
60
80
100
120
Discharge Capacity (%) (Nominal Capacity Ratio)
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NICKEL METAL HYDRIDE BATTERIES - CONTINUED
•
Discharge temperature characteristics at 1C discharge
Self-discharge is affected by the temperature at
which the batteries are left standing and the length of
time during which they are left standing. It increases
in proportion as the temperature or the shelf-standing
time increases. Panasonic’s nickel-metal hydride
batteries have excellent self-discharge
2.0
Charge
: 1CmA x 1.2h
1.8
Temperature: 20˚C
Model
: HHR160A
1.6
1.4
20˚C
characteristics that are comparable to those of Ni-Cd
batteries.
1.2
1.0
0.8
-10˚C
Cycle Life Characteristics
0˚C
The cycle life of these batteries is governed by the
conditions under which they are charged and dis-
charged, temperature and other conditions of use.
Under proper conditions of use (example: IEC charge
and discharge conditions), these batteries can be
charged and discharged for more than 500 cycles.
0.6
0
20
40
60
80
100 120
140
160
Charge Capacity (%) (Nominal Capacity Ratio)
•
Discharge temperature characteristics
•
Cycle life characteristics
120
100
120
100
Temperature : 20˚C
Model : HHR160A
1C
80
3C
60
80
40
Charge
: 1CmA x 1.2h
60
40
Temperature: 20˚C
Discharge : Cut-off Voltage 1.0V
20
0
Model
: HHR160A
-20
-10
0
10
20 30
40
50
20
0
100
200
300
400
500
Discharge Temperature (˚C)
Number of Cycles (cycle)
Storage characteristics
These characteristics include self-discharge
characteristics and restoration characteristics after
long-term storage. When batteries are left standing,
their capacity generally drops due to self-discharge,
but this is restored by charge.
Safety
When the internal pressure of these batteries rises
due to overcharge, short-circuiting, reverse charge or
other abuse or misuse, the self-resealing safety vent
is activated to prevent battery damage. Panasonic’s
nickel-metal hydride batteries have similar safety
characteristics as Panasonic Ni-Cd batteries.
•
Self discharge characteristics
100
90
Temp.: 20˚C
80
Ni-MH (HHR160A)
70
60
Temp.: 45˚C
Ni-Cd (P-120AS)
50
Charge
: 1CmA x 1.2h
40
30
Discharge: 1CmA to 1.0V/cell
0
1
2
3
4
Storage Period (weeks)
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